The invention is directed to an infusion system having a control device for automatically adapting the dosage of drugs to the multi-factorial influences of the patient's condition which can change over time.
In many cases, infusion of drugs is an indispensable therapeutical measure for maintaining the vital functions of the human organism. Particularly during extracorporeal purification of the blood in patients suffering from; chronic kidney diseases, or after extensive surgical interventions or in case of large blood loss due to injuries, the frequent complications are characterized by multi-factorial influences with high non-linearities. Although the mechanisms of the effects of the individual factors are known in qualitative terms, hardly any clearance has been achieved concerning their complex interaction. Thus, typically, knowledge on the causal interdependencies underlying the complications is largely fuzzy.
Due to their deterministic control characteristics and the associated algorithms, numerous infusion systems are restricted to the crisp (deterministic) knowledge on the control mechanisms of the human organism.
In many known cases, the control devices are used on the basis of a black-box model which is valid under stationary conditions or quasi-stationary conditions. Therefore, such control devices react insufficiently or not at all on the spontaneous sensitivity changes of the endogenous regulatory system. Further disadvantages arise in processes involving long idle times, as normally occurring in the human organism during infusion of drugs.
In other known infusion systems, use is made of control structures having adaptive properties. In these systems, the adapting of the infusion rate to the varying condition of the patient is performed through fixedly predetermined algorithms, which partially even allow predictions on the period up to the onset of the drug's effect. The algorithms have been obtained on the basis of individual components of influence of the multi-factorial control mechanisms. Therefore, control devices of the above type provide useful results only as long as the underlying causal connections are really decisive for the current effect of the drug infusion.
However, as apparent from medical practice, complications occurring in the human organism often have their origin in qualitative changes occurring in the complex interaction of multi-factorial components. These phenomena can be represented only as fuzzy (probabilistic) information in the form of probabilistic relations and linguistic variables.
Thus, applications of the above kind require infusion systems adapted to detect and evaluate a plurality of different components of influence in the form of fuzzy information and to involve these components in the automatic controlling of the dosage of drugs corresponding to their semantic significance. This applies particularly to medical applications such as extracorporeal blood purification wherein additional components of influence will result directly from the intended therapeutical purposes of the treatment. In such applications, the interaction between the dosage of the drug and the target parameters of the treatment, such as ultrafiltration rate, overall dehydration, sodium balance and other important control parameters, must be continuously observed.
Due to their deterministic structure, the above outlined known control devices are not suited to fulfill these demands.
Some known blood pressure control devices, used in surgery for monitoring purposes during and after a surgical intervention, are designed for processing fuzzy knowledge on the basis of fuzzy logic (H. Ying et al, "Expert-system-based fuzzy control of arterial pressure by drug infusion", in: Medical Progress through Technology, Kluner Academic Publishers, Dordrecht, Netherlands, 198, pp. 203 thru 215).
Also fuzzy control devices of this type do not meet the above demands for the following reasons: The medical purpose of blood pressure control consists exclusively in keeping the blood pressure constant during and after a surgical intervention. The blood pressure and values derived therefrom, such as a deviation from the desired value of the blood pressure (error) and the change over time of these deviations (rates), are the only criteria used for the operation of the fuzzy control device. Thus, control is restricted to a sole semantic domain. Additional influence factors caused by a simultaneously performed therapeutical measure are left unconsidered.
Therefore, it is an object of the invention to provide an infusion system comprising a control device which actively includes a plurality of influence values having different physiological action mechanisms, i.e. a plurality of semantic domains, into the automatic dosing of drugs as fuzzy information and which, in doing so, takes into account the different semantic significances of the different domains.